The public is turning to the web for information on swine flu. Photograph: Oleg Popov/Reuters

What are people talking about online?

Tracking conversations and trends online has become something of a craft since social media took off, and it's a powerful way to pick up on breaking news and what has captured the public imagination. Why, one Susan Boyle was the most common term on Twitter for more than a week - before being beaten down by swine flu.

There's a swathe of social media "monitoring" tools being pushed by rather annoying marketing firms obsessed with tracking "buzz" about a brand or product.

For a web-savvy news organisation, top trending terms on sites like Twitter and Google's search trends can dictate the news agenda too - watch what people want to read about, and do quick turnaround news stories to meet that demand.

But this week, it's all about swine flu. "Swine flu symptoms" is the most searched-for term on the Guardian site today, while Swine Flu, #swineflu and Mexico are the most common terms on Twitter, where the subject accounted for 2% of all messages yesterday, according to Nielsen.

While that reflects public interest and the news agenda, it also highlights how many of us turn to the web as our first source of information. The web is famously treacherous as a self-diagnosis tool; a perfect example of how a little information can be dangerous; some Twitter users have been spreading message about not eating pork (it's not possible to catch swine flu from eating infected meat). It's amazing that this needs spelling out, but it's clearly better to rely on information from reliable sources, like the Centre for Disease Control and Prevention, rather than what someone calling themselves @budgiebreath says on Twitter.

Evgeny Morozon on Foreign Policy is rather po-faced about what he calls "Twitter's role in facilitating an unnecessary global panic". As ever, Twitter is reflecting real-world behaviour and not driving it. He reels off eight irresponsible tweets but takes them all without context; if anyone you followed had posted any of these, wouldn't you have taken them to task?

@page_1215: "I'm concerned about the swine flu outbreak in us and mexico could it be germ warfare?"

@villageteaco: "Swine flu? Wow. All that pork infecting people....beef and chicken have always been meats of choice"

"If my reading list on Twitter was only restricted to the individuals who had produced the posts above, by now I would be extremely scared and probably feeling a great urge to post a scary Twitter update myself," he writes. That's a very big "if" though - most of us don't follow a whole group of idiots - and are also capable of recognising a joke when we see one.

"In moments like this, one is tempted to lament the death of broadcasting, for it seems that the information from expert sources – government, doctors, and the like – should probably be prioritised over everything else and have a higher chance of being seen that the information from the rest of one's Twitter-feed, full of speculation, misinformation, and gossip."

Elsewhere on the web there are just such sources, and with increasingly imaginative ways of presenting a continuous flow of information. The Global Disease Alert Map, for example.

Google set up a dedicated flu watch service late last year and claims it picks up on flu outbreaks two weeks ahead of monitoring techniques used by the healthcare profession. It's a simple enough idea; people search for flu-related advice and treatment online when they are ill or worried that they are about to become ill. Overlay Google's search data with that of the Centre for Disease Control, which handles data from 16 million patients across the US, and there's a direct correlation.

The Seattle startup Veratect specialises in picking up on trends like this, and claims it spotted the breakout in Mexico before government health authorities by monitoring social media and combining that with official reports. What they do differently is put men on the ground, hiring local analysts to contextualise their data.

According to Google, however, flu-related searches are relatively low today, which is probably a reflection of how Twitter is more a social tool (there are plenty of light-hearted swine-flu related quips in there) and Google for more in-depth research. Swine flu was only 42 in the Google's most-searched for terms in the US today.